Sulfur dioxide plant

ABSTRACT

Production of sulfur dioxide by means of the combustion of sulfur and pure oxygen in a closed system that produces a high yield in the recovery of SO 2  and reduces environmental contamination to levels below the standard requirements. Sulfur dioxide is produced by burning sulfur and pure oxygen diluted in recirculated combustive gas that has been previously cooled in order to maintain combustion at less than 1200° C. The gaseous mix thus obtained would be comprised of approximately 16% V/V oxygen and 84% V/V of SO 2 . This latter percentage makes it very easy to liquefy SO 2  so that a 95% SO 2  recovery efficiency would be obtained at −10° C. The non-liquefied gas is recirculated in a closed system. The SO 2  content in the 84% V/V SO 2  gas could even be liquefied at 20° C., at 5 bar, thus increasing the system&#39;s efficiency even further.

SPECIFICATION

[0001] Sulfur is generally burned with dry air in a combustion chamber in the production of sulfur dioxide, obtaining a gas of 80% V/V of nitrogen, 18% V/V of SO₂, the rest being oxygen and inert gases. This gas is then liquefied at a temperature of −50° C. at a pressure of 0.8 bar. Greater pressure is required to liquefy this product at a higher temperature. The SO₂ recovery efficiency achieved through the liquefaction of this gas is approximately 75%. The rest of the non-liquefied SO₂ gas and the excess oxygen not burned and other inert gases must be eliminated from the process line. If this mix is discharged into the atmosphere, the contamination is heavy and a costly neutralization procedure is required to reduce contamination.

[0002] The proposed invention patent application refers to a process to obtain sulfur dioxide by means of the combustion of sulfur and pure oxygen, which produces gas in a concentration exceeding 80% V/V 0f SO₂, without any inert gases to discharge into the atmosphere, which reduces environmental contamination to levels below those required by standards. That high concentration of SO₂ also allows for a better SO₂ recovery yield due to liquefaction.

[0003] In the proposed process, the elemental sulfur is smelted and maintained at 140° C. At that temperature it has a viscosity appropriate to its pumping into the sulfur burner. The combustion of smelted sulfur is done in a boiler combustion chamber with pure oxygen diluted in cold combustion gas. This latter gas comes from the recirculation of a fraction of the combustion gas obtained that may contain some unused oxygen. The purpose of this recirculation is to maintain the gas leaving the combustion chamber at less than 1200° C. since otherwise the combustion of sulfur and pure oxygen in stoichiometric quantities would produce an excessively high temperature (more than 5000° C.). The combustion gas thus obtained has around 80% V/V of SO₂.

[0004] The gas from the combustion chamber is cooled to 180° C. by its passing through the boiler, which produces steam at 4 bar that is used as a means of heating in the sulfur liquefaction tanks.

[0005] The combustion gas passes through an air-cooled heat interchanger where it is cooled to 80° C., after which it passes through a sulfuric acid absorption tower where it is cooled to room temperature and moisture and sulfur particles are eliminated. The sulfuric acid used in the tower is maintained at room temperature using a water-cooled heat interchanger. The gas, thus purified, is passed through a sulfuric acid drop trap.

[0006] To this point, the entire line described is at a negative pressure since the gases circulate by suction from the blower that pushes the gas mass towards the combustion furnace (70-95% of the mass) and towards the cooling plant (remaining 5-30%).

[0007] Liquid SO₂ is obtained from the cooling plant and a non-condensable gaseous mix of SO₂ and unused oxygen that is suctioned by the negative pressure from the blower. The drop in temperature helps reduce the temperature of the gas recirculated to the boiler even further. The entire gas circulation system is thus made in a completely closed circuit.

[0008] Given the high concentrations of SO₂ produced, high SO₂ recovery efficiencies could be obtained by liquefaction in a cooling plant, depending on the different operating pressure and temperature conditions of the plant. For example, it is possible to achieve a 95% recovery of the SO₂ contained in 80% SO₂ gas at 20° C. and 0.8 bar. That same recovery is possible with 80% SO₂ gas at 20° C. and 3.4 bar.

[0009] For a better explanation of the invention, a description is provided below of a preferred embodiment in relation to FIG. 1, which shows a generic preferred process diagram.

[0010] As appreciated in FIG. 1, flows 1 and 2 correspond to sulfur and pure oxygen, respectively. The sulfur in the flow line is smelted in heat interchanger 3 and continues toward the sulfur burner in boiler 4. The combustion gas obtained in the boiler, displaced by suction from blower 7, passes to an air interchanger 5 and then continues through a purifier and cooler 6. From blower 7, the mass of gas is driven towards the fork point 8, where part is conveyed to mixing point 9, and the oxygen fed in 1 is incorporated to convey the mix thus enriched towards boiler 4. The remaining mass of gas at fork point 8 is conveyed to cooling plant 10. The product current 11 is obtained there in the form of liquid SO₂ and a non-condensable gaseous mix that is suctioned by the negative pressure of blower 7 and returned to the circuit via mixing point 12. 

What is claimed is:
 1. A process to obtain sulfur dioxide by means of the combustion of sulfur and pure oxygen, characterized in that the elemental sulfur is smelted and maintained at 140° C., the temperature at which it has a viscosity appropriate for its pumping to the sulfur burner. The smelted sulfur combustion occurs in the combustion chamber of a boiler with pure oxygen diluted in cold combustion gas that comes from the recirculation of a fraction of the combustion gas obtained that may contain some unused oxygen. The purpose of said recirculation is to maintain the gas leaving the combustion chamber at a lower temperature. The gas is cooled in the combustion chamber to 180° C. by passing it through the boiler, which produces steam at 4 bar that is used as a means of heating in the sulfur liquefaction tanks. The combustion gas then passes through a sulfuric acid absorption tower where it is cooled and moisture and sulfur particles are eliminated. Said sulfuric acid used in the tower is kept at room temperature by means of a water-cooled heat interchanger. The gas thus purified is passed through a sulfuric acid drop trap. All of the above occurs at a negative pressure since the circulation of the gases occurs by suction from the blower that drives the mass of gas towards the combustion furnace and towards the cooling plant. Liquid SO₂ is obtained at the cooling plant and a non-condensable gaseous mix of SO₂ and unused oxygen that is suctioned by the negative pressure of the blower. Its drop in temperature helps reduce the temperature of the gas recirculated to the boiler even further and the entire gas circulation system is conducted in a completely closed circuit.
 2. A process according to claim 1, characterized in that the elemental sulfur is smelted and then combusted with pure oxygen diluted in cold combustion gas and the gas leaving the combustion chamber is kept at a temperature of less than 1200° C.
 3. A process according to claim 1, characterized in that the combustion gas obtained is preferably 80% SO₂.
 4. A process according to claim 3, characterized in that the combustion gas is purified and cooled to a temperature close to room temperature.
 5. A process according to claim 1, characterized in that 70% to 95% P/P of the purified and cooled combustion gas is recirculated to the combustion furnace, after enrichment with pure oxygen to maintain the combustion.
 6. A process according to claim 1, characterized in that around 20% of the purified and cooled combustion gas is sent to the cooling plant to obtain liquid SO₂ and a non-condensable gaseous mix of SO₂ and unused oxygen that is suctioned by the negative pressure of the blower whose low temperature helps reduce the temperature of the gas recirculated to the combustion furnace even further, thus configuring a gas circulation system in a completely closed circuit.
 7. A process according to claim 1, characterized in that it reduces environmental contamination to levels below those required by standards and has a better yield in obtaining SO₂. 